The present invention relates generally to digital-to-analog converters and more particularly to a circuit for expanding the resolution of such converters.
In many control applications it is necessary to convert a digital signal, such as the output of a computer, to an analog equivalent in order to effect control. There are, of course, commercially available digital-to-analog converters (hereinafter referred to as DAC's) capable of performing this function. However, it is often desired to control a voltage to a greater degree of precision that is possible with present-day commercially-available DAC's. For example, while there are such converters available having as high as 12-bit or even 16-bit monotonic resolution (i.e., successive steps of an increasing signal are of substantially equal non-deteriorating increments), it would be desirable to have converters having as much as 18-bit to 22-bit performance. As a consequence, various techniques have been proposed to increase the resolution of the available converters. Some of these proposals include multiple DAC's with read-only memory-based correction circuits, and voltage or current regulation schemes to provide additional bits. However, such proposals have generally resulted in circuits that are cumbersome and expensive.